As a vibration isolator such as an engine mount that bears the vibration of a vibration source, such as an automobile engine, so as to not be transmitted to a vehicle body side, a liquid-sealed vibration isolator is known which includes a first fixture attached to the vehicle body side, a second fixture attached to the vibration source side, a vibration isolating base interposed between the fixtures and constituted by a rubber-like elastic body, a main liquid chamber in which a portion of a chamber wall is formed by the vibration isolating base, a subsidiary liquid chamber in which a portion of a chamber wall is formed by a diaphragm, and an orifice flow path through which the liquid chambers communicate with each other.
In such a liquid-sealed vibration isolator, when a normal vibration is input, a vibration damping function and a vibration isolation function are, fulfilled by a liquid column resonance action due to a fluid flow in the orifice flow path and a vibration control effect of the vibration isolating base. However, when a large vibration is input, the vibration isolator itself becomes a generation source of abnormal noise which is transmitted into the vehicle interior in some cases.
The abnormal noise is generated by cavitation in the liquid chamber. Cavitation is a phenomenon caused by the fact that, when a large vibration is input into the vibration isolator, the orifice flow path is clogged, whereby the inner portion of the main liquid chamber enters an excessive negative pressure state and falls below the saturated vapor pressure of the sealed liquid, and a large number of bubbles are generated. Moreover, the impact sound, which is generated when the bubbles generated in this manner are extinguished, becomes an abnormal noise and is transmitted to the outside.
Thus, in order to prevent the generation of abnormal noise due to cavitation, for example, PTL 1 mentioned below discloses that a short-circuit path performing short-circuiting of the main liquid chamber and the subsidiary liquid chamber is provided in a partitioning member partitioning both liquid chambers, a valve main body switching the short-circuit path into a communication state and a closed state is formed by a metal spring such as a plate spring, whereby, when the main liquid chamber enters the excessive negative state, the short-circuit path is opened to supply liquid from the subsidiary liquid chamber to the main liquid chamber. Furthermore, as mentioned below, PTL 2 also discloses a configuration in which the same valve main bodies are held by the spring.
Furthermore, as mentioned below, PTL 3 discloses a configuration which has a function as a check valve by providing a movable membrane in a partitioning body partitioning the main liquid chamber and the subsidiary liquid chamber, providing a slit-like opening portion functioning as a valve main body in a part of the movable membrane, and offsetting the arrangement of the valve main body portion to the subsidiary liquid chamber side with respect to a valve main body displacement restriction member.